[sdiy] bypass caps, subbing MLCC for Electrolytic

[Paul Perry]

The ESR of both the electronic and ceramic caps behave quite
differently as you move up the frequency range - though I expect
a MLCC behaves much smoother than one of those horrible little
blue things on legs at high frequency.
Anyway, what anyone with a power supply SHOULD do, and
nobody I know (including myself) does, is to hit it with square
waves and look for ringing.
One can argue for hours, but actually seeing ringing on the power
 rails - or not - that's pretty convincing.

paul perry Melbourne Australia


----- Original Message ----- 
From: "Tony Rolando" <tony at makenoisemusic.com>
To: "Harry Bissell" <harrybissell at wowway.com>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, October 06, 2010 6:35 AM
Subject: Re: [sdiy] bypass caps, subbing MLCC for Electrolytic


>  Well in the case of this App Note (and others), all of the 10uF
> electrolytics are paired with a .1uF ceramic, which would have the lower
> ESR, so wouldn't that defeat the purpose of the higher ESR on the 10uF?
>
> T
>
> On 10/5/10 3:32 PM, Harry Bissell wrote:
>> I have seen an app note for a switching power supply chip which
>> said that electrolytics might be preferred because of their
>> inherently higher ESR. too low of a value would make their
>> chip unstable.  OTOH they did say you could arrange to have higher ESR by 
>> adding a series
>> resistor or equivalent length of circuit trace (which might be bad for
>> other reasons)
>>
>> I forget whether it as a Linear Tech part, or Maxim. I used the Linear 
>> Tech with the
>> ceramic caps.
>>
>> Ceramic caps could be an advantage for board manufacture, there is no 
>> polarity to
>> get wrong (and explode - tantalum :^)
>>
>> H^) harry
>>
>> ----- Original Message -----
>> From: Tony Rolando<tony at makenoisemusic.com>
>> To: Harry Bissell<harrybissell at wowway.com>
>> Cc: David G. Dixon<dixon at interchange.ubc.ca>, synth-diy at dropmix.xs4all.nl
>> Sent: Tue, 05 Oct 2010 14:24:34 -0400 (EDT)
>> Subject: Re: [sdiy] bypass caps, subbing MLCC for Electrolytic
>>
>>    Thanx for the insights guys. David, it is the diameter. I could put a
>> 1206 MLCC in the same spot.
>>
>> Harry, I was going to use either X7R or X5R, 1206 MLCC. The ap note for
>> the IC (PCM1807 ADC) did specify Electrolytic, but did not say why... I
>> suppose I am wondering what the electrolytic could offer that the MLCC
>> could not. Perhaps as you noted the lower ESR could be "bug" in this
>> case. I just prefer MLCC since they are longer life and not polarized.
>>
>> Texas Instruments had the following to say this morning when I ask this
>> same question:
>>
>> "They (electrolytics) are used in relatively high-current and
>> low-frequency electrical circuits, particularly in power supply filters,
>> where they store charge needed to moderate output voltage and current
>> fluctuations in rectifier output. They are also widely used as coupling
>> capacitors in circuits where AC should be conducted but DC should not.
>>
>> So, they were particularly recommended for their ability to better block
>> DC, and moderate output voltage. If you aren't worried too much about
>> these characteristics, then it should be fine to use the ceramic 
>> versions."
>>
>>
>> I've never heard anybody say electrolytic blocks DC better?
>>
>>
>> Tony
>>
>>
>>
>> On 10/5/10 12:37 PM, Harry Bissell wrote:
>>> The ceramic caps are just fine for bypassing, except in some
>>> critical switching power supply designs that might specify to
>>> USE ONLY electrolytic or USE ONLY MLCC (depends on whether the ESR
>>> is a "bug" or a "feature"
>>>
>>> Ceramics are nice in that they take high SMT temperatures, and are
>>> inherently non-polar.  Watch out for the dielectric... some like
>>> Y5V (there is a cap in the circuit, its size is basically unknown and 
>>> you don't care...)
>>> are really crap (Z5U is not much better). I prefer X7R if they would
>>> be small enough...
>>>
>>> H^) harry
>>>
>>>
>>> ----- Original Message -----
>>> From: David G. Dixon<dixon at interchange.ubc.ca>
>>> To: 'Tony Rolando'<tony at makenoisemusic.com>, synth-diy at dropmix.xs4all.nl
>>> Sent: Tue, 05 Oct 2010 12:26:34 -0400 (EDT)
>>> Subject: Re: [sdiy] bypass caps, subbing MLCC for Electrolytic
>>>
>>>>     Hello, Has anybody ever had any problems subbing a MLCC type cap 
>>>> for
>>>> an electrolytic in a bypass situation? Low ESR is not required. 16V 
>>>> 10uF
>>>> Electrolytic was called, I'd like to use 16V 10uF MLCC in order to save
>>>> space.
>>> I use 10uF electrolytics in this application which are only about 0.2" 
>>> in
>>> diameter and about 0.5" high, and have 0.1" lead spacing.  Is it the
>>> diameter or the height that you are worried about?
>>>
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